RIP Wayne Guest

[garydubbs]

i was watching the following video on youtube about gold testing and wondered if anyone has done the same with thai gold and/or knows the speed of sound through thai gold?

is it the same as pure gold at 3240m/s? i'd imagine slightly different due to the differing pureness?

[cloudhopper]

The technology is explained here - http://www.olympus-ims.com/en/applications/ut-testing-gold-bars/

[Soutpeel]

The technology is explained here - http://www.olympus-i...ting-gold-bars/

The techniques and equipment shown are used more commonly for assesing the quality and integrity in welds and other materials, and yes this could be an application, however a word of caution on the velocity method, even two samples of 99.9 gold may give you slightly different velocity values the 3240 m/s given is not an absolute...

I would be pretty confident you could distingish 99.9 gold from say 18 kt gold due to the copper content and other alloys increasing, but would see a difference between 99.9% and 97% gold...most likely not as the changes in velocity would be so small.

The other thing, this kit could be used for "bad" as well unless you really know what your looking at as regards ultrasonics, someone could manipulate the kit to read what ever they wanted it to read...in other words someone could convince someone that what the equipment says is 99.9% gold could be something less because some one has "messed" with the settings

Nice idea but I would be very careful and if you are thinking of doing this yourself hope you have some cash to spend, industrial ultrasonic equipment such as the pulse echo kit shown start at about US10k upwards, a probe/cable will set you back something like US$ 1000

And of course forgot to mention how you would beat a velocity measurement like this...in the gold bar incorperate a cheaper material with the same velocity as gold and you will see no change

Edited October 11, 2012 by Soutpeel

[cloudhopper]

And of course forgot to mention how you would beat a velocity measurement like this...in the gold bar incorperate a cheaper material with the same velocity as gold and you will see no change

What material might that be? Any refraction caused by an interface between the pure gold exterior and the internal material will show up clearly on the time domain scope.

[Soutpeel]

And of course forgot to mention how you would beat a velocity measurement like this...in the gold bar incorperate a cheaper material with the same velocity as gold and you will see no change

What material might that be? Any refraction caused by an interface between the pure gold exterior and the internal material will show up clearly on the time domain scope.

Your correct using pulse echo kit in your link you would see an interface echo between the materials on the A-scan (time domain trace)...I was talking about using only a velocity measurement which in video this is all this kit does it appears...it gives you a number.

As regards which materials, velocities for various material are not internationally standardised, ie they are not absolutes, for example cast iron's dependent on which velocity table you use can vary from around 3000m/s anywhere upto 5000m/s dependent on the alloys in the material, Some loaded composites are in the 3200-3300 m/s range...the difference between 3200m/s and 3240m/s - 40m/s difference aint much, of course this may pass a velocity test, but would fail one of the other tests..ie like weighing the bar

The point I am getting at is that somewhere there is a material with the same velocity of as gold and one shouldnt just rely on a test like this to confirm something is what somebody claims it to be, this test would be complementary to existing tests and shouldnt be used in isolation

It is a good idea in applying different technology, but one shouldnt just rely on this test as being definitive...its not

Edited October 11, 2012 by Soutpeel

[garydubbs]

some good stuff, thanks guys. do any of you know what the common sound speed in thai gold is?

[Soutpeel]

some good stuff, thanks guys. do any of you know what the common sound speed in thai gold is?

I dont think you will find that info commonly availible, as one supposes no has done this in Thailand, but if you really want to know for what ever reason, go an find an NDT company in Thailand who does industrial ultrasonic's

You will need to provide with a piece of Thai gold which is known to be the purity your after, you need measure the thickness quite accurately, something 12.5mm thick with parallel faces, will work the best and get them to use an ultrasonic thickness gauge and calibrate to the known thickness by adjusting the instrument velocity until the digitial read out is the same at the measured thickness on your sample...this is the velocity of your sample.

If you want even more accurate need two samples of same of differing thickness say 6.35mm and 12.5mm calibrate on an A-scan flaw dectector calibrate so both thickness are reading correctly..velocity used is the sample velocity

You could then take the average between the two velocites and this would be your "common" velocity any further samples of unknown material would be measured against this standard

Edited October 11, 2012 by Soutpeel

[kwonitoy]

The first thing I learned about UT (Ultrasonic Testing) is that if you don't calibrate your set your readings are useless.

Didn't notice any calibrations to check the probe or meter's accuracy

I sure wouldn't buy any gold that had been "verified" by a D meter.

Using the Omniscan phased array in the link by cloudhopper would be the preferred way

If someone could loan me a gold bar I can take it to work and run the phased array over it.

I'll bring it back, honest

[Soutpeel]

If someone could loan me a gold bar I can take it to work and run the phased array over it.

I'll bring it back, honest

I agree the size of the test piece should be at least the size of a V1 block...

On on the D-meter thing...asolutely useless without a cal block and that kit in the video appears just to be a stock meter, with a panametric's or KK twin

Edited October 11, 2012 by Soutpeel

[ajarnpot]

If you have the money for this tester, why not use conductivity test, acid tests, lead assay? I think its a useful tool to a point, but conductivity is more accurate? if you are interested in testling pm me

[Soutpeel]

If you have the money for this tester, why not use conductivity test, acid tests, lead assay? I think its a useful tool to a point, but conductivity is more accurate? if you are interested in testling pm me

I think you missing the purpose of a velocity test...it looks at the volume of the sample, ie its homogenus throughout the same, surely a conductivity test...assuming you mean electrial conductivity would only give you answer for the surface of the same ?

The point being there are multiple tests that shoudl be conducted to ensure you are getting what your paying for, this velocity test is not intended to replace all the other tests but compliment them

[ajarnpot]

If you have the money for this tester, why not use conductivity test, acid tests, lead assay? I think its a useful tool to a point, but conductivity is more accurate? if you are interested in testling pm me

I think you missing the purpose of a velocity test...it looks at the volume of the sample, ie its homogenus throughout the same, surely a conductivity test...assuming you mean electrial conductivity would only give you answer for the surface of the same ?

The point being there are multiple tests that shoudl be conducted to ensure you are getting what your paying for, this velocity test is not intended to replace all the other tests but compliment them

nah conducitivty through sample determined by dimensions etc. not over surface.............. why am I bothering to explain something on tv.......

but yeah, many tests exist

[Soutpeel]

why am I bothering to explain something on tv.......

give it try... ....as one assumes you are talking about electrical conductivity based on an IACS standard or similar

[ajarnpot]

oh, fair enough...from the look of your posts you look to be engineer type....or consultant.....not corrossion or piping though I guess,

conducitivity through the sample, dependent on dimensions losses due to less conductive materials will show up, of course losses due to contact made to the gold in the first place will be significant and need to be factored in, but I assume a commercial meter has this calibrated already,

I guess changes in material would be noticed by ultrasound, but its not the cheapest answer

best way, , melt it all down, remove impurities, then craft your very own shapes and sell it on at a premium,

something topical, like a bunny rabbit for the year of rabbit or similar

Edited October 17, 2012 by ajarnpot

[Soutpeel]

oh, fair enough...from the look of your posts you look to be engineer type....or consultant.....not corrossion or piping though I guess,

conducitivity through the sample, dependent on dimensions losses due to less conductive materials will show up, of course losses due to contact made to the gold in the first place will be significant and need to be factored in, but I assume a commercial meter has this calibrated already,

I guess changes in material would be noticed by ultrasound, but its not the cheapest answer

best way, , melt it all down, remove impurities, then craft your very own shapes and sell it on at a premium,

something topical, like a bunny rabbit for the year of rabbit or similar

In your explanation of what your talking about I believe you are getting things a tad mixed up....conductivity and resistivity are reciprocal's and are inherant in a specific material and is the measure of specfic material to conduct an electric current.

These values are not influenced by volume of the material or changes in cross section of the material.

I beleive what you are taking about is infact a resistance measurement as you mention a change in dimension, as the resistance value considers the resistivity and the cross sectional area of the sample.

I havent seen the instrument you refer to, but one assumes its an eddy current based unit, which has an AC excitation on the test coil, which will be limited on its test depth into tha material by a property called SDP (standard depth of penetration) or some times know as skin effect, therefore if you were testing a gold bar you would only be testing upto a certain distance below the surface not the complete volume of the sample

Ultrasonic testing and this test measure completely different properties of the material, Ultrasonic testing measures a property known as acoustic impedance while eddy current testing (if this is what this kit is) basically measures changes in the electrical impedance ie inductive reactance versus resistance

I will leave it there as we are getting into some "heavy" topic's which went out my career many years ago and are no long part of my job

unless you want to get into the mathamatics of this...which will result in a rather boring topic...

BTW I do know a few things about corrosion and piping..

Edited October 17, 2012 by Soutpeel

[ajarnpot]

ha ha, but none the less reciprocal or not, you can measure losses IR losses through the entire bar. Based on dimensions you can estimate what you expect fquite easily and any large losses ( once you've accounted for contacts) can be atrributed to impurities, gold is a great conductyor which is why it in your computer , mobile ipad etc etc.

[Soutpeel]

ha ha, but none the less reciprocal or not, you can measure losses IR losses through the entire bar. Based on dimensions you can estimate what you expect fquite easily and any large losses ( once you've accounted for contacts) can be atrributed to impurities, gold is a great conductyor which is why it in your computer , mobile ipad etc etc.

Duh..gold is good conductor of electricity...I did not know that...please detail your methodology then and I will comment further...The problem I have here is the words your using estimate, large losses etc, i hope you are not basing your assupmtions on introducing a current into sample and using a multi-meter to try and estimate impurities in a sample ?

Your responses to date are very lacking in any sort of technical detail, so please give the details then and I will comment further

[cloudhopper]

This is just a theoretical question but will the DC resistance measured between 2 faces of a bar change with other dimensions well beyond the probed region? eg would two 1cm-thick plates measure the same resistance between faces at the center if one plate was 50X50 and the other 100X100?

Anyway if I had a gold shop I'd go with the phased array.

Edited October 17, 2012 by cloudhopper